The purpose of the experiment was to assess the response of 10-kg pigs to diets containing increasing levels of dietary lysine when formulated on a digestible amino acid and ideal protein basis. The experiment consisted of a growth study and a nitrogen retention study. A basal diet which contained 4.8 g digestible lysine per kilogram and 3.6 Mcal DE was supplemented with 0, 2.0, 2.4, 3.6, 4.8 or 6.0 g of lysine per kilogram for a concentration of 4.8, 6.0, 7.2, 8.4, 9.6 or 10.8 g digestible lysine per kilogram of diet, respectively. Forty-eight crossbred pigs with an average body weight of 10 kg were blocked by weight and randomly assigned to the six experimental diets for a 28-d growth study. Increasing digestible lysine levels resulted in linear (P<.05) and quadratic (P<.05) responses in average daily gain (ADG) and feed efficiency (FE). Mean ADG and FE ranged from 287 to 549 g and 262 to 508 g/kg, respectively, for the six diets. A quadratic effect was observed for average feed intake (P<.05) and ranged from 1003 to 1275 g. Twenty-four crossbred pigs with an average body weight of 15 kg were blocked by weight, randomly assigned to the six experimental diets and maintained in metabolism crates for a 10-d nitrogen balance study. No treatment effects (P>.05) were observed for nitrogen absorption while a linear (P<.05) response was observed for nitrogen retention (NR) and ranged from 11.97 to 14.30 g/d for the six diets. No further improvement in nitrogen retention was observed beyond 7.2 g of digestible lysine per kilogram of diet. Analysis of the ADG and FE data using the broken-line method yielded a digestible lysine requirement of 7.2 and 7.1 g digestible lysine per kilogram of diet, respectively. Analysis of the NR data using the broken-line method estimated the requirement to be 7.8 g digestible lysine per kilogram of diet.
